2006 Texas Cell Phone Pilot Study

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					Reducing Bias Through a Bimodal Data
             Collection
  2006 Texas Cell Phone Pilot Study

       Michelle L. Cook, M.P.H.
           March 27, 2007



                                       1
Background
BRFSS interviews are on residential
landlines only
More households are becoming cell phone
only households
Harder to reach and collect data on younger
respondents



                                              2
                                    Age Distributions in the 1990's
                         1993 Texas BRFSS vs. 1990 Census Texas Population
    30

                              24.9 25.4
    25
                                              22.3
                                                     20.9
    20

                  15.6                                                                        15.2
                                                               14.5                                  14.1
%




    15     13.4                                                       13.4
                                                                                      10.6
                                                                                9.7
    10


    5


    0
         18 - 24 Years      25 - 34 Years   35 - 44 Years    45 - 54 Years    55 - 64 Years   65+ Years
                                                       Age Group

                              1993 Texas BRFSS (Unweighted)           1990 Texas Census

                                                                                                      3
                                    Age Distributions in 2005
                           Texas BRFSS vs. Estimated Texas Population
    25
                                                                                              23.1

                                    20.4            20.6
    20                                       18.6             19.0 19.0
                                                                              17.2
                             15.7
    15           13.8                                                                                13.4
                                                                                     12.7
%




    10
           6.4

    5



    0
         18 - 24 Years     25 - 34 Years   35 - 44 Years    45 - 54 Years   55 - 64 Years     65+ Years
                                                      Age Group

                        2005 Texas BRFSS (Unweighted)       2005 Estimated Texas Population

                                                                                                      4
2006 Texas Cell Phone Pilot
Study Objectives
To capture younger adults via cell phone
To reduce bias in the Texas BRFSS using a
bimodal approach




                                            5
Methods




          6
Questionnaire Changes
2006 Texas Cell Phone Pilot Study
  Number of residential lines
  Number of adults living in their household
  If a student, did they live in on-campus housing
  State currently living in
  Abbreviated 2006 BRFSS questionnaire used
2006 Texas BRFSS (November/December)
  Number of personal cell phones

                                                     7
2006 Cell Phone Pilot Study
Statewide sample (no stratification)
English interviewing only
Cell phones were called mainly on weekends and
evenings from 7pm-9pm.
Made sure respondent was in a safe place (e.g., not
driving a car).
Made sure the respondent was an adult.
Timeframe: November 2006 – February 2007

                                                      8
Cell Phone Pilot Study:
Disposition Recodes
Dataset sent had 298 interviews
2 respondents answered all questions as “refused”
(recoded as 220)
2 respondents started questionnaire but didn’t
finish (recoded as 210)
7 respondents were students living in dorms
(recoded as 420)
13 respondents were living in a different state
(recoded as 405)
TOTAL # OF INTERVIEWS: 274
                                                    9
2006 Texas BRFSS
13 strata which included 3 African
American oversamples
Only November/December files used in this
analysis
Spanish and English interviewing
  98 Spanish interviews were removed before
  merging the two datasets.
TOTAL # OF INTERVIEWS: 1,323

                                              10
Demographic Differences of the
Respondents
2006 Nov/Dec BRFSS      2006 Cell Phone Pilot
  3.7% aged 18-24 yrs     25.5% aged 18-24 yrs
  34.8% Male              51.5% Male
  17.5% Hispanic          26.8% Hispanic




                                                 11
Combining Data Sources
269 cell phone respondents matched to the
appropriate 2006 geographic stratum based
on self-reported county code.
5 respondents placed into a geographic
stratum based on their reported age.
  Remaining Metropolitan Counties (younger)
  All Other Non-Core Counties (older)


                                              12
Re-Weighting
wt_prob took into account access to both
residential phone numbers and personal cell
phones.
If (denstr=1) wt1=wt_prob
If (denstr=2) wt1=wt_prob*1.5
If (denstr=3) wt1=wt_prob*2.87
Poststrafied by age (3) and gender.

                                              13
Results




          14
              Prevalence of Fair/Poor General Health by Survey
                 2006 Texas BRFSS & Cell Phone Pilot Study
    25



    20



    15
%




    10
                                       17.6
            15.9
                                                                  13.7
     5



     0
         Merged File              Nov/Dec BRFSS              Cell Phone Pilot
                                     Survey


                                                                                15
                        Prevalence of Obesity by Survey
                   2006 Texas BRFSS & Cell Phone Pilot Study
    40

    35

    30

    25
%




    20

            30.7                        32.2
    15                                                              29.8

    10

     5

     0
         Merged File               Nov/Dec BRFSS               Cell Phone Pilot
                                       Survey

                                                                                  16
                    Prevalence of Current Smokers by Survey
                   2006 Texas BRFSS & Cell Phone Pilot Study
    25



    20



    15
%




    10                                                              19.3
            17.7                        18.5


     5



     0
         Merged File               Nov/Dec BRFSS               Cell Phone Pilot
                                       Survey

                                                                                  17
                  Age-Adjusted Estimates by Phone Status
              2006 Merged Texas Cell Phone Pilot Study and BRFSS
                   Only Landline                 Both                    Only Cell
n                        374                     963                       107
                   %           95% CI      %           95% CI      %             95% CI
General Health,
                  31.0    (24.9 - 37.9)   10.8     (8.4 - 13.8)   21.9       (12.3 - 35.9)
Fair/Poor
5+ Days of
Physical Health   26.3    (20.4 - 33.1)   15.3    (11.6 - 19.9)   24.0       (14.0 - 38.0)
Not Good
5+ Days of
Activity          24.4    (17.4 - 33.1)   9.0      (6.0 - 13.4)   12.5       (5.1 - 27.4)
Limitations
Current Smoker    20.2    (14.7 - 27.0)   15.0    (12.1 - 18.6)   32.0       (20.4 - 46.4)
Obesity           40.9    (32.9 - 49.5)   28.0    (23.8 - 32.7)   36.0       (24.1 - 49.8)



                                                                                     18
Limitations
Response rate (CASRO) low for Cell Phone Pilot.
  2006 Cell Phone Pilot Study: 5.7%
  2006 Nov/Dec BRFSS (includes Spanish): 44.9%
Cell phone sampling did not occur based on
BRFSS geographic strata (the 2.87 assumption).
Questions added to each survey could be tailored
for better understanding.
Don’t know what percentage of households
overlapped between the two studies.
  Were some of the refusals people who already
  participated in the landline survey or vice versa?
                                                       19
Discussion
Since an estimated 74.1% of adults in Texas
had both a cell phone and a landline phone,
17.0% had only a landline, and 9.0% had
only a cell phone, is it worth it?




                                              20
Thanks
Macro International, Inc.
  James J. Dayton, MBA
  Naomi L. Freedner, MPH
  Amy S. Ayotte
  Kisha M. Bailly
  Kristie M. Hannah
Texas Department of State Health Services
  Rebecca A. Wood, MSHP
  Anna Vincent
  Jennifer Haussler, MS

                                            21